The European Centre for Disease Prevention and Control reported in the annual risk assessment released on Tuesday that circulation of the flu during the 2013-2014 season started late in Europe.
The assessment reports that timing of the illness has been different across European countries. The first affected by influenza were Bulgaria, Greece, Portugal and Spain. Without a specific geographic pattern, the virus spread through the continent quickly, reaching its peak during the first weeks of 2014 in Bulgaria, Portugal and Spain.
Influenza activity continues to increase in Greece, according to the risk assessment.
The assessment reports the A(H1)pdm09 strain was dominant or codominant in 21 countries. In four countries, A(H3) was dominant. The ECDC said the difference may be attributed to prior exposure to the strains or higher rates of vaccination among the population.
The ECDC said influenza vaccines have been a "good match" for the common strains. North American studies of the virus estimate high to moderate effectiveness.
A study from Navarre, Spain reported lower effectiveness for the flu vaccine. The ECDC said the discrepancy warrants further studies to understand the mitigating factors.
The ECDC said countries that experienced a peak of A(H1)pdm09 may see a later peak of the A(H3) strain, and vice versa.